[Recommended Hardware?]

Don't worry about power consumption, even with decent hardware its minimal.

 

Id get a G4650 cpu with an b250 or h270 motherboard with 6 sata ports for expansion, 4-8gb ddr4 ram and that should be enough for multiple 1080p transcodes and basically anything else you want to do.

[Drivers requests for DSM 5.2]

How about hdhomerun dvbhdhomerun linux driver?

 

Would be great for plex and tversity

 

http://sourceforge.net/apps/trac/dvbhdhomerun/

[How update DSM 4.3-3810 UPDATE 3]

Have you tried the script used to update to update2?

[Recommendations for a Mini-ITX build]

I can confirm the i217 on the H87i-plus and some other h87 chipset boards works perfectly.

[Recommendations for a Mini-ITX build]

Are you sure the h87i-plus nic doens't work? Its the intel 217

 

The latest changelog says

 

NETWORK

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Update INTEL e1000e driver to v2.5.4 (support I217x and I218x chip)